This invention relates to a semiconductor device, and especially to a semiconductor device in which a bipolar transistor and a MIS FET are formed in an epitaxial growth layer on the same semiconductor substrate and to a method of manufacturing the above device.
Though an integrated circuit device which comprises a bipolar transistor capable of conducting a large current and a MIS FET having a high input impedance, has many advantages with regard to circuit design, the process of manufacturing it is very complicated, so that there are many difficulties in putting it into practical use.
For example, in a prior art integrated semiconductor circuit of the above-mentioned type, disclosed in Japanese Patent Laid-Open No. 51-148380, it is necessary to place it in a furnace for about thirty minutes at a high temperature of about 1100.degree. C. to form a gate insulating film of a MIS FET. Since this process is carried out after the emitter diffusion of a bipolar transistor, the emitter diffusion is still progressing in this process, and consequently the current amplification factor h.sub.FE of the bipolar transistor is changed from a desired value. Therefore, there is a problem in that it is difficult to control the current amplification factor h.sub.FE of the bipolar transistor at a desired value.
Thus, there is proposed a method of manufacturing a semiconductor device in which after the formation of the gate insulating film, the formation of the emitter region is effected at a temperature (for example 1000.degree. C.) lower than the formation temperature of the gate insulating film. However, in the above-mentioned method, there are problems in that when the gate insulating film is thin (for example, below 1000 .ANG.) the impurity used for the emitter diffusion is diffused into the surface of the semiconductor substrate through the insulating film. In addition the thickness of the gate insulator film is changed and therefore it becomes difficult to control the threshold voltage V.sub.TH of the MIS FET at a desired value. Therefore, in order to put the above-mentioned method into practical use, it is necessary to improve it still more.